Matt says that the only difference between the two tags is that that <strong> tag refers to presentation, while the <b> tag is a semantic label. But he reminds us that in practice they both do the same thing, every browser just uses the tags to make text bold.
The difference between the two HTML tags is that bold makes text only visually look bold, while strong also semantically emphasizes the respective text as important and indicates that it is a meaningful word or text section.